Summary of significant accounting policies - Revenue by Geographic Areas (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Total revenues	$ 46,931	$ 38,755	$ 88,085	$ 70,965
U.S. revenues
Disaggregation of Revenue [Line Items]
Total revenues	46,931	30,351	88,085	56,398
Foreign revenues
Disaggregation of Revenue [Line Items]
Total revenues	$ 0	$ 8,404	$ 0	$ 14,567